The present invention relates in general to multicolor, sheet-fed rotary printing machines consisting of a plurality of consecutively arranged press units each having a plurality of sheet-processing cylinders and gear trains for interconnecting the press units. In particular, this invention relates to a hydrualic driving device for use with such a printing machine.
From prior art, a driving device for printing machines of the above type is known, for example from the DD patent 90 799, in which the individual press units of the printing machine are interconnected by gear trains and driven by hydraulic motors. In order to differentiate the torque of the hydraulic motors, a control unit is provided including pressure-reducing valves or flow control valves for varying the working conditions of the machine.
The disadvantage of such known drives employing hydraulic motors in connection with preset valves is a relatively costly installation and operation. Moreover, such known drives are not suitable for all kinds of operational modes required for multi-color printing machines. Particularly, they are unsuitable for speed adjustment in the range from 1 to 100 for reducing the speed to a slow run with 1.5 rotations per minute to the full rotary speed required for the machine. Also, the prior-art drives do not meet the requirement of a uniformly high torque at a constant rotary speed necessary for ensuring a good quality of the print.
Still another disadvantage of such conventional hydraulic drives for printing machines is their incapability of achieving a jerk-free start during an intermittent or stepwise mode of operation.